The invention generally relates to a laminate as well as a device and a method for manufacturing a laminate. More specifically, the invention relates to a laminate composed sequentially of an amorphous or polycrystalline substrate, a textured buffer layer, and an oriented oxide thin layer. The invention is also based on a device for manufacturing laminate with a vacuum chamber in which positioning devices for a substrate and buffer layer material dispensing devices for providing a buffer layer as a substrate for an oriented thin layer on the substrate are so arranged that buffer layer material is capable of being evaporated from the buffer layer material dispensing devices at an angle xcex11xe2x89xa00 to the normal to the substrate surface, onto the latter, as well as a method for manufacturing laminate whereby a buffer layer is applied to a substrate, with the buffer layer material being evaporated from the buffer layer material dispensing devices at an angle xcex11xe2x89xa00 to the normal to the substrate surface onto the latter, before an oriented thin layer is evaporated as a way of manufacturing monocrystalline thin layers on polycrystalline or amorphous substrates.
To produce monocrystalline thin layers of a specific material, the material is generally applied to suitable monocrystalline substrates of another material. The substrates must have a suitable lattice structure in order to permit so-called heteroepitaxy, in which the monocrystalline structure of the substrate is assumed by the layer applied. This method is also used to produce thin layers of high-quality oxide high-temperature superconductors for example, such as YBa2Cu3O7-d (YBCO). In such superconductors, grain boundaries can drastically deteriorate the superconducting properties. Grain boundaries with a large grain boundary angle have a greater effect than those with a small angle between the crystal axes of the grains involved. The effect of the grain boundaries is obvious from a comparison of the critical current densities. This value is 3 to 5 MA/cm2 in YBCO at 77 K on monocrystalline substrates in an intrinsic magnetic field. Typically, only 0.02 MA/cm2 is reached on nontextured substrates. For this reason, a monocrystalline structure of the superconductor is required when manufacturing high-quality, high-temperature superconductor layers.
The method of manufacturing high-quality superconductor layers by heteroepitaxial growth on monocrystalline substrates is limited to relatively small areas since such substrates are available only up to a very limited size. In addition, monocrystalline substrates are very expensive and therefore not economical in many cases. In particular it is not possible to make strips of monocrystals that are the prerequisite for power cables or wound magnets made of high-temperature superconductors.
Recently a number of approaches have been taken to circumvent the limitation to monocrystals. By using suitable methods, a quasi-monocrystalline or especially a biaxial texture is created in the substrate itself or in a buffer layer that is deposited on the substrate. This means that the crystal axes of the substrate or possibly of the buffer layer are aligned with a certain degree of unsharpness that is generally characterized by one or more half-width values. Then, in a second step for example, the superconductor is applied heteroepitaxially to this substrate or buffer layer. In this way, for example, improved superconducting properties are achieved, such as an increase in critical current density. This increases inversely with the half-width value or values of the buffer layer. Four important methods of producing a biaxial structure have been published.
Thus a method has been developed in which a biaxial texture is produced in nickel strips by multiple rolling followed by recrystallization (Rolling Assisted Biaxially Textured Substrates: RABiTS(copyright)), as published in A. Goyal et al., APL 69, Page 1795,1996. However, a superconductor cannot be applied directly to these nickel strips since nickel does not have a substrate suitable for direct deposition of a superconductor due to diffusion and oxidation problems. Therefore a diffusion barrier is produced by a complex series of buffer layers grown epitaxially on it to produce a surface suitable for deposition of superconductors, on which surface the high-temperature superconductor layer then grows epitaxially. It is disadvantageous in this method that nickel is unsuitable for many applications because of its deficient tensile strength. In addition, the ferromagnetism of nickel is disadvantageous in applications involving a magnetic field.
In so-called xe2x80x9cIon Beam Assisted Depositionxe2x80x9d (IBAD) according to Y. Iikama et al., APL 60, page 769, 1992, the buffer layer is bombarded with low-energy ions as it is being deposited on a substrate, at a sharp angle. Y2O3-stabilized zirconium dioxide (YSZ) is usually employed as the buffer layer material. This method allows biaxially textured layers of high quality to be produced that permit deposition of superconducting films for example with very good properties. However the cost of the apparatus is high because an ion source is used, the deposition rate is low, and the deposition area is limited by the ion source. These points are cost-intensive and make the IBAD method unsuitable for commercial applications.
Another method is laser deposition at sharp angles (Inclined Substrate Deposition: ISD) as described in K. Hasegawa et al., Proc. of ICEC 16, 1996, Kitakyushu, Japan, and EP 669 411 A2. Depending on the deposition conditions, during laser deposition on a noninclined substrate, a crystal axis is set perpendicular to the substrate surface and hence parallel to the deposition direction. If the normal of the substrate is then inclined relative to the deposition direction, this crystal axis follows the deposition direction. At a suitable inclination angle, a second crystal axis is also oriented parallel to the surface and the biaxial texture is obtained. However, the laser deposition method is less suited for economical large-area coating because of the limited size of the area that can be coated at one time.
Similarly, a biaxial texture has been produced in thin metal layers by evaporating aluminum from resistance-heated boats (cf. T. Hashimoto et al., Thin Solid Films 182, 197, 1989). A background pressure of 4xc3x9710xe2x88x925 mbar was used during deposition. The degree of texturing was poor, however. In addition, metals in general and aluminum in particular are not suitable as substrates for direct deposition of a superconductor because of diffusion and oxidation problems and a lack of thermal stability.
The goal of the present invention is to produce a laminate that is improved over the prior art and to improve devices and methods for manufacturing a laminate.
This goal is achieved by the features in described herein for a laminate and a device and a method for manufacturing a laminate.
Thus, a laminate according to the invention with a sequence composed of an amorphous or polycrystalline substrate, a textured buffer layer, and an oriented thin layer is characterized by at least one cover layer being contained between the buffer layer and the thin layer.
The at least one cover layer according to the invention means that gape and irregularities in the buffer layer caused by manufacture are smoothed out so that the oriented oxide thin layer has a high quality that corresponds to the surface of the cover layer that is available to it for growth, said quality being expressed in particular in a critical current density when the oriented thin layer is an oxide high-temperature superconductor thin layer. However, qualitatively improved layer structures are according to the invention are also achieved for other similar thin layers.
To the extent that reference has been made above and will be made below to high-temperature superconductors, this is to be understood as only an example. The invention is suitable without limit in general for any other oriented, preferably oxide or metal, thin layers that in particular can have a technical functional layer such as, in addition to an already mentioned high-temperature superconductor layer for example a YBCO layer, a ferromagnetic layer, including such a ferromagnetic layer with so-called xe2x80x9cGiant Magneto Resistance,xe2x80x9d or a ferroelectric layer. Another possibility is to have a plurality of oriented thin layers placed one on top of the other above the at least one cover layer.
It is preferable for the material for the buffer layer to be evaporated onto the substrate surface at an angle xcex11xe2x89xa00 to the normal to the latter and preferably in addition for the material for the cover layer to be evaporated onto the buffer layer under deposition conditions different from those under which the buffer layer was applied, especially at a different pressure, a different temperature, a different rate and/or a different angle xcex12xe2x89xa0xcex11, preferably xcex12 less than xcex11, especially xcex12≈0xc2x0, to the normal to the substrate surface. According to additional preferred embodiments, the buffer layer can have a biaxial texture and/or facets.
Preferably materials for the buffer layer and at least one cover layer contain oxide material including MgO, CeO2, Y2O3 stabilized zirconium oxide (YSZ). Provision can also be made for the substrate to have a metal or metal alloy surface with an amorphous or polycrystalline structure that faces the oriented thin layer and is in particular polished and/or heat-resistant, whereby in particular the substrate itself and/or the surface contains thermally oxidized silicon, a nickel-based alloy such as Hastelloy C(copyright), partially Y2O3 stabilized ZrO2 (PSZ), heat-resistant stainless steel, platinum, and/or Al2O3, each in the polycrystalline or amorphous form. For example an untextured Al2O3 layer can form the surface of the substrate, thus acting as a protective layer. In this way for example a diffusion barrier layer including an oxidation barrier layer, a smoothing layer, and/or a layer with an adhesion promoter can be produced in an advantageous manner.
In a device for manufacturing laminate, with a vacuum chamber in which positioning devices for a substrate and buffer laminate material dispensing devices for forming a buffer layer as a substrate for an oriented oxide thin layer on the substrate are arranged in such fashion that buffer layer material can be evaporated from the buffer layer material dispensing devices at an angle xcex11xe2x89xa00 to the normal to the substrate surface, onto the latter, with such a device being referred to hereafter as according to the genus, the goal of the invention can be achieved by virtue of the fact that cover layer material dispensing devices for forming at least one cover layer as a substrate for the oriented thin layer on the buffer layer are provided as well as equipment by means of which the material for the cover layer can be evaporated onto the buffer layer under deposition conditions that are different from those under which the buffer layer was applied, especially at a different pressure, a different temperature, a different rate, and/or a different angle, whereby possibly the cover layer material dispensing devices in particular are arranged relative to the substrate positioning devices in such fashion that cover layer material can be applied to the buffer layer at an angle xcex12xe2x89xa0xcex11 preferably xcex12 less than xcex11, especially xcex12≈0xc2x0, to the substrate surface normal.
Further embodiments of the invention in terms of devices can include, as an alternative to or in addition to the above design, devices for thermal evaporation, especially electron beam evaporation or reactive evaporation, of buffer layer material, possibly of the cover layer material and/or the material for the oriented thin layer.
To achieve the goal that forms the basis of the invention, either together with each of the above embodiments or alone, a device according to the genus can be improved in such fashion that the angle xcex11 is larger, especially slightly larger, than an angle xcex2 that a crystal axis of the buffer layer material forms with the substrate surface normal, with another crystal axis of the buffer layer material being parallel to the substrate surface.
Another improvement on the device according to the genus is likewise suitable for achieving the goal of the invention, whereby devices for producing and maintaining a pressure that is higher by comparison to the rest of the vacuum chamber are provided in the vicinity of the application of the buffer layer material and possibly of the cover layer material and/or the material for the oriented oxide thin layer on the respective substrate. These features can possibly be combined with the above versions.
Instead of or in addition to the above-mentioned pressure increase, reactive materials or components such as radicals, ions, more reactive molecular compounds than those available or desired in the evaporated material are present in a layer formation area.
The simple pressure increase is generally viewed as a quantitative solution because of the large number involved and a simple use of reactive materials or components can be viewed as a qualitative solution because active particles are produced.
In a device according to the genus defined above, the goal of the invention can also be achieved alternatively or additionally by virtue of the fact that in the area where the buffer layer material, and possibly the cover layer material and/or the material for the oriented oxide thin layer, is applied to the respective substrate, devices are provided for adding components that are volatile during the evaporation of the respective material or materials and/or components that are required for producing the buffer layer and possibly the cover layer and/or the oriented oxide thin layer, and/or reactive components in gas form. A material supply of this kind is accomplished in particular by means of an area of increased pressure as described above. In addition to or instead of replacement of materials that are volatile during evaporation, materials are used by means of which reactive evaporation is achieved. For example a pure metal can be evaporated and oxygen can be added during the pressure increase so that an oxide layer is formed. As another example H2 can be added in order to change the preferred growth directions. Generally speaking, a surfactant can be added.
Improvements on the devices according to the invention described above can comprise the following:
I. That the substrate positioning devices are possibly designed such that the substrate is located in a first layer formation area (a) inclined with respect to the horizontal such that the buffer layer material that rises at least approximately perpendicularly to the horizontal from the buffer layer material dispensing devices reaches the substrate in the first layer formation area at an angle xcex11xe2x89xa00 to the normal to the substrate surface, or (b) is located at least approximately parallel to the horizontal, and the buffer layer material dispensing devices are arranged relative to the first layer formation area such that buffer layer material that rises at an angle to the horizontal from the buffer layer material dispensing devices reaches the substrate in the first layer formation area at an angle xcex11xe2x89xa00 to the normal to the substrate surface, and/or
II. That the substrate positioning devices are possibly so designed that the substrate with the buffer layer is located at an angle to the horizontal at least in a second layer formation area (a) so that cover layer material that rises at least approximately perpendicularly to the horizontal from the cover layer material dispensing devices reaches the buffer layer on the substrate at least approximately at an angle xcex12, preferably xcex12xe2x89xa0 xcex11, especially xcex12 less than xcex11, and preferably xcex12≈0, to the normal to the substrate surface, or (b) is located at least approximately parallel to the horizontal, and the cover layer material dispensing devices are so arranged, and the cover layer material dispensing devices are so located relative to the second layer formation area, that cover layer material that rises at an angle to the horizontal from the cover layer material dispensing devices reaches the buffer layer on the substrate in the second layer formation area at least approximately at an angle xcex12, preferably xcex12xe2x89xa0xcex11, especially xcex12 less than xcex11, preferably xcex12≈0xc2x0 to the normal to the substrate surface.
Provision can be made for other advantageous improvements on the invention such that the substrate positioning devices contain a substrate holder for substrates moving on it and/or a substrate guide for substrates that are conveyed continuously in the form of strips or cables.
In particular, the devices for producing and maintaining a pressure that is higher than that in a conventional vacuum chamber can be arranged so that in a layer formation area or in an area where a layer or partial layer has already been formed, a pressure is maintained that is higher than that in the rest of the vacuum chamber, with particular provision being made for multiple passage through a pressure-increasing device and/or successive passages through a plurality of pressure-increasing devices with evaporation stations located in between.
It is also preferable for the pressure-increasing devices possibly to be so designed that they can produce, in a layer formation area or in an area where the layer or a partial layer has already been formed, a pressure of at least approximately xe2x89xa75xc3x9710xe2x88x924 mbar, especially at least approximately xe2x89xa71xc3x9710xe2x88x923 mbar relative to a pressure of approximately xe2x89xa61xc3x9710xe2x88x924mbar, preferably xe2x89xa62xc3x9710xe2x88x925 mbar at the source.
Preferably, the above devices are designed for making laminates according to the invention.
The method produced by the invention is based on the following steps: application of a buffer layer to a substrate, with the buffer layer material being evaporated from buffer layer material dispensing devices at an angle xcex11xe2x89xa00 to the normal to the substrate surface onto the latter, followed by evaporation of an oriented thin layer on top of that.
On this basis, according to the invention, according to which, following the evaporation of the buffer layer and prior to the evaporation of the oriented thin layer, at least one cover layer is evaporated under deposition conditions that are different from those under which the buffer layer was applied, especially at a different pressure, a different temperature, a different rate and/or different angle xcex12xe2x89xa0xcex11, preferably xcex12 less than xcex11, especially xcex12≈0xc2x0, to the substrate surface normal, and/or onto the buffer layer in such fashion that the buffer layer has a biaxial texture and/or facets.
Alternatively or in addition, the buffer layer material, the cover layer material, and/or the material for the oriented oxide thin layer can be thermally evaporated for application to the respective substrate, for example by electron beam evaporation, or can be applied reactively.
Further approaches to achieving the goal of the invention consist in angle xcex11 being larger, especially slightly larger than an angle xcex2 that a crystal axis of the buffer layer material forms with the substrate surface normal, with another crystal axis of the buffer layer material being parallel to the substrate surface.
In addition, the method according to the invention can include, in addition to the basic steps, a pressure that is higher by comparison to the other vacuum conditions prevailing in the area of application of the buffer layer material and possibly the cover layer material and/or the material for the oriented oxide thin layer on the respective substrate.
Of course it is also possible to achieve the goal of the invention in such fashion that in the area of application of the buffer layer material and possibly the cover layer material and/or the material for the oriented oxide thin layer, volatile components and/or components required for producing the buffer layer, possibly the cover layer, and/or the oriented oxide thin layer and/or reactive components in gas form is/are added to the respective substrate during evaporation of the respective material or materials.
As regards the pressure increase and/or the presence of certain materials or particles in the layer formation area, reference is made regarding the possibilities and effects to the corresponding information above in the description of the corresponding device features.
These methods can also be improved by the oriented thin layer being an oxide or metal thin layer and/or a technical functional layer, especially a high-temperature superconductor layer, preferably a YBCO layer, a ferromagnetic layer, including such a ferromagnetic layer with so-called xe2x80x9cgiant magneto resistance,xe2x80x9d or a ferroelectric layer, and in that preferably a plurality of oriented thin layers are applied one over the other on top of the at least one cover layer.
Other improvements in the method provide that the buffer layer and/or at least one cover layer contain oxide material including MgO, CeO2, Y2O3 stabilized zirconium oxide (YSZ) or at least consist largely of these materials and/or that the substrate has a metal or metal alloy surface facing the oriented thin layer and being in particular polished and/or heat-resistant, said metal or metal alloy surface having an amorphous or polycrystalline structure, whereby preferably the substrate itself and/or the surface contains or contain thermally oxidized silicon, a nickel-based alloy such as Hastelloy C(copyright), partially Y2O3 stabilized ZrO2 (PSZ), heat-resistant stainless steel, platinum, and/or Al2O3, each in a polycrystalline or amorphous form.
Possible improvements in the above methods can consist firstly in arranging the substrate at least in a first layer formation area (a) at an angle to the horizontal such that buffer layer material that rises at least approximately perpendicularly to the horizontal from the buffer layer material dispensing devices reaches the substrate in the first layer formation area at an angle xcex11xe2x89xa00 to the normal to the substrate surface or (b) is located at least approximately parallel to the horizontal and buffer layer material is evaporated relative to the first layer formation area in such fashion that buffer layer material that rises at an angle to the horizontal from the buffer layer material dispensing devices reaches the substrate in the first layer formation area at an angle xcex11xe2x89xa00 to the normal to the substrate surface, and/or that on the other hand the substrate together with the buffer layer is located at an angle to the horizontal in at least one second layer formation area (a) such that the cover layer material that rises at least approximately perpendicularly to the horizontal from the cover layer material dispensing devices, in the second layer formation area, reaches the buffer layer on the substrate at least approximately at an angle xcex12, preferably xcex12xe2x89xa0xcex11especially xcex12 less than xcex11, preferably xcex12xe2x89xa00xc2x0 to the normal to the substrate surface, or (b) is located at least approximately parallel to the horizontal, and cover layer material is evaporated relative to the second layer formation area such that cover layer material that rises at an angle to the horizontal from the cover layer material dispensing devices in a second layer formation area reaches the buffer layer on the substrate at least approximately at angle xcex12, preferably xcex12xe2x89xa0xcex11, especially xcex12 less than xcex11, preferably xcex12≈0xc2x0 to the normal to the substrate surface.
It is also possible in the method according to the invention that substrate material in the form of strips or cables can be conveyed continuously or that a substrate is mounted movably.
Provision can also be made within the framework of the invention such that, possibly in a layer formation area or in an area where the layer or a partial layer has already been formed, a pressure is produced or maintained that is higher than under usual vacuum conditions, whereby in particular multiple passages are made through a pressure-elevating device and/or successive passages are made through a plurality of pressure-elevating devices with evaporating stations located in between.
Further alternatives to or combinations with the above variations can be achieved in a method according to the invention by possibly providing, in a layer formation area or in an area where a layer or partial layer has already been formed, a pressure of at least approximately xe2x89xa75xc3x9710xe2x88x924 mbar, especially at least approximately xe2x89xa71xc3x9710xe2x88x923 mbar, relative to a pressure of approximately xe2x89xa61xc3x9710xe2x88x924 mbar, preferably xe2x89xa62xc3x9710xe2x88x925 mbar at the source.
Preferably the methods according to the invention serve to produce the laminate described at the outset.
In the case of the laminate as well as the manufacturing device and the manufacturing method for the laminate, a simple and rapid, i.e. economical manufacture of textured buffer layers for superconductor coating is made possible. In addition, the buffer and cover layers can also be applied over large areas continuously. Furthermore, the texture can be applied to a biaxially textured surface on the superconductor.